1# OpenLDAP: pkg/openldap-guide/admin/maintenance.sdf,v 1.7.2.10 2010/04/13 20:22:34 kurt Exp
2# Copyright 2007-2010 The OpenLDAP Foundation, All Rights Reserved.
3# COPYING RESTRICTIONS APPLY, see COPYRIGHT.
4
5H1: Maintenance
6
7System Administration is all about maintenance, so it is only fair that we
8discuss how to correctly maintain an OpenLDAP deployment.
9
10
11H2: Directory Backups
12
13Backup strategies largely depend on the amount of change in the database
14and how much of that change an administrator might be willing to lose in a
15catastrophic failure. There are two basic methods that can be used:
16
171. Backup the Berkeley database itself and periodically back up the transaction
18log files:
19
20Berkeley DB produces transaction logs that can be used to reconstruct
21changes from a given point in time. For example, if an administrator were willing to only
22lose one hour's worth of changes, they could take down the server in
23the middle of the night, copy the Berkeley database files offsite, and bring
24the server back online. Then, on an hourly basis, they could force a
25database checkpoint, capture the log files that have been generated in the
26past hour, and copy them offsite. The accumulated log files, in combination
27with the previous database backup, could be used with db_recover to
28reconstruct the database up to the time the last collection of log files was
29copied offsite. This method affords good protection, with minimal space
30overhead.
31
32
332. Periodically run slapcat and back up the LDIF file:
34
35Slapcat can be run while slapd is active. However, one runs the risk of an
36inconsistent database- not from the point of slapd, but from the point of
37the applications using LDAP. For example, if a provisioning application
38performed tasks that consisted of several LDAP operations, and the slapcat
39took place concurrently with those operations, then there might be
40inconsistencies in the LDAP database from the point of view of that
41provisioning application and applications that depended on it. One must,
42therefore, be convinced something like that won't happen. One way to do that
43would be to put the database in read-only mode while performing the
44slapcat. The other disadvantage of this approach is that the generated LDIF
45files can be rather large and the accumulation of the day's backups could
46add up to a substantial amount of space.
47
48You can use {{slapcat}}(8) to generate an LDIF file for each of your {{slapd}}(8)
49back-bdb or back-hdb databases.
50
51>    slapcat -f slapd.conf -b "dc=example,dc=com"
52
53For back-bdb and back-hdb, this command may be ran while slapd(8) is running.
54
55MORE on actual Berkeley DB backups later covering db_recover etc.
56
57H2: Berkeley DB Logs
58
59Berkeley DB log files grow, and the administrator has to deal with it. The
60procedure is known as log file archival or log file rotation.
61
62Note: The actual log file rotation is handled by the Berkeley DB engine.
63
64Logs of current transactions need to be stored into files so that the database
65can be recovered in the event of an application crash. Administrators can change
66the size limit of a single log file (by default 10MB), and have old log files
67removed automatically, by setting up DB environment (see below). The reason
68Berkeley DB never deletes any log files by default is that the administrator
69may wish to backup the log files before removal to make database recovery
70possible even after a catastrophic failure, such as file system corruption.
71
72Log file names are {{F:log.XXXXXXXXXX}} (X is a digit). By default the log files
73are located in the BDB backend directory. The {{F:db_archive}} tool knows what
74log files are used in current transactions, and what are not. Administrators can
75move unused log files to a backup media, and delete them. To have them removed
76automatically, place set_flags {{DB_LOG_AUTOREMOVE}} directive in {{F:DB_CONFIG}}.
77
78Note: If the log files are removed automatically, recovery after a catastrophic
79failure is likely to be impossible.
80
81The files with names {{F:__db.001}}, {{F:__db.002}}, etc are just shared memory
82regions (or whatever). These ARE NOT 'logs', they must be left alone. Don't be
83afraid of them, they do not grow like logs do.
84
85To understand the {{F:db_archive}} interface, the reader should refer to
86chapter 9 of the Berkeley DB guide. In particular, the following chapters are
87recommended:
88
89* Database and log file archival - {{URL:http://www.oracle.com/technology/documentation/berkeley-db/db/ref/transapp/archival.html}}
90* Log file removal - {{URL:http://www.oracle.com/technology/documentation/berkeley-db/db/ref/transapp/logfile.html}}
91* Recovery procedures - {{URL:http://www.oracle.com/technology/documentation/berkeley-db/db/ref/transapp/recovery.html}}
92* Hot failover - {{URL:http://www.oracle.com/technology/documentation/berkeley-db/db/ref/transapp/hotfail.html}}
93* Complete list of Berkeley DB flags - {{URL:http://www.oracle.com/technology/documentation/berkeley-db/db/api_c/env_set_flags.html}}
94
95Advanced installations can use special environment settings to fine-tune some
96Berkeley DB options (change the log file limit, etc). This can be done by using
97the {{F:DB_CONFIG}} file. This magic file can be created in BDB backend directory
98set up by {{slapd.conf}}(5). More information on this file can be found in File
99naming chapter. Specific directives can be found in C Interface, look for
100{{DB_ENV->set_XXXX}} calls.
101
102Note: options set in {{F:DB_CONFIG}} file override options set by OpenLDAP.
103Use them with extreme caution. Do not use them unless You know what You are doing.
104
105The advantages of {{F:DB_CONFIG}} usage can be the following:
106
107* to keep data files and log files on different mediums (i.e. disks) to improve
108  performance and/or reliability;
109* to fine-tune some specific options (such as shared memory region sizes);
110* to set the log file limit (please read Log file limits before doing this).
111
112To figure out the best-practice BDB backup scenario, the reader is highly
113recommended to read the whole Chapter 9: Berkeley DB Transactional Data Store Applications.
114This chapter is a set of small pages with examples in C language. Non-programming
115people can skip these examples without loss of knowledge.
116
117
118H2: Checkpointing
119
120MORE/TIDY
121
122If you put "checkpoint 1024 5" in slapd.conf (to checkpoint after 1024kb or 5 minutes,
123for example), this does not checkpoint every 5 minutes as you may think.
124The explanation from Howard is:
125
126'In OpenLDAP 2.1 and 2.2 the checkpoint directive acts as follows - *when there
127is a write operation*, and more than <check> minutes have occurred since the
128last checkpoint, perform the checkpoint. If more than <check> minutes pass after
129a write without any other write operations occurring, no checkpoint is performed,
130so it's possible to lose the last write that occurred.''
131
132In other words, a write operation occurring less than "check" minutes after the
133last checkpoint will not be checkpointed until the next write occurs after "check"
134minutes have passed since the checkpoint.
135
136This has been modified in 2.3 to indeed checkpoint every so often; in the meantime
137a workaround is to invoke "db_checkpoint" from a cron script every so often, say 5 minutes.
138
139H2: Migration
140
141The simplest steps needed to migrate between versions or upgrade, depending on your deployment
142type are:
143
144.{{S: }}
145^{{B: Stop the current server when convenient}}
146
147.{{S: }}
148+{{B: slapcat the current data out}}
149
150.{{S: }}
151+{{B: Clear out the current data directory (/usr/local/var/openldap-data/) leaving DB_CONFIG in place}}
152
153.{{S: }}
154+{{B: Perform the software upgrades}}
155
156.{{S: }}
157+{{B: slapadd the exported data back into the directory}}
158
159.{{S: }}
160+{{B: Start the server}}
161
162Obviously this doesn't cater for any complicated deployments like {{SECT: MirrorMode}} or {{SECT: N-Way Multi-Master}},
163but following the above sections and using either commercial support or community support should help. Also check the
164{{SECT: Troubleshooting}} section.
165
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167